Cyanobacteria and heterotrophic bacteria have been clubbed together in Eubacteria of kingdom Monera as per the "Five Kingdom Classification" even though the two are vastly different from each other. Is this grouping of the two types of taxa in the same kingdom justified? If so, why?

As per the "Five Kingdom Classification" cyanobacteria that are autotrophic organisms are clubbed together with heterotrophic bacteria in Eubacteria of kingdom Monera. This grouping of the two types of taxa in the same kingdom is correct. This is because both cyanobacteria and heterotrophic bacteria are unicellular and prokaryotes.